The invention is directed to a method for optically measuring electrical potentials.
The method known from Electronics Letters, Vol. 21, No. 13 (1985), pages 568-579, incorporated herein, uses a crystal plate having electro-optical properties, and which is dielectrically mirrored on one side in order to image the distribution of potential in microelectronics components with the assistance of a laser probe. Since the measuring sensor scanned point-by-point by the probe is arranged immediately above the component, the electrical stray fields emanating from the interconnects can penetrate into the crystal and induce birefringence therein. The change in the polarization of the laser radiation which penetrates the crystal in the region of the stray field that is thereby caused is documented in an analyzer unit and registered, dependent on the location of the laser focus on the component surface.
Whereas the measuring method known from Electronics Letters, Vol. 20, No. 20 (1984), pages 818 and 819, from Appl. Phys. Letters 47 (10), 1985, pages 1083-1084 and from U.S. Pat. No. 4,681,449, all incorporated herein, utilizes the electro-optical properties of the substrate material for registering changes in signal level in GaAs circuits, the method described in Electronics Letters, Vol. 22, No. 17 (1986), pages 918-919, incorporated herein, uses a LiTaO.sub.3 crystal tip in order to stroboscopically sample the electrical fields occurring in the region of the interconnects with the assistance of a laser probe which penetrates the crystal tip.
Further laser measuring methods are disclosed in IEEE Journal of Quantum Electronics, Vol. 22, No. 1, 1986, pages 69-78, incorporated herein.